Laminated magnetic core joint structure



Aug. 30, 1966 L. A.V JEAN ETAL LAMINATED MAGNETIC CORE JOINT STRUCTURE l I l l Laurent'. mberf Jennclecmsd.; Maxime Louis Emile Jen!! and Michel M arcd Jean,

ai 'i'ni'i` ngenxfrs and as Ct mls rn rs Laurent Hlberl Jean.

Eff/JMU Aug. 30, 1966 l.. A. JEAN ETAL LAMINATED MAGNETIC CORE JOINT STRUCTURE Filed Nov. 12. 1965 2 Sheets-Sheet 2 FIG 9 gcuss United States Patent O 3,270,307 LAMINATEI) MAGNETIC CORE JOINT STRUCTURE Laurent Albert Jean, deceased, late of Dun-sur-Auron, Cher, France, by Maxime Louis Emile Jean, 32 Rue de la Republique, Saint-Germain-en-Laye, France, and Michel Marcel Jean, 12 Rue Dnpetit-Thouars, Paris, France, administrators Filed Nov. 12, 1963, Ser. No. 323,168 Claims priority, application France, Nov. 10, 1962, 915,006 13 Claims. (Cl. 336-217) The present invention relates to the field of laminated magnetic circuits for electrical apparatus such as transformers or machines, and more particularly to transformers comprising at least one rectangular core element aving two legs designed to received transformer windings and yokes or cross-members joining the winding legs together at their extremities.

Such magnetic circuits are generally constructed by the stacking of sheets which have been suitably cut for the purpose of assembling them in successive layers. At present one preferably uses sheets which are said to have oriented grains which present in a preferential direction, corresponding to the direction of their lamination, a permeability which is greater than the permeability presented in any other direction, and which sheets will have losses, expressed in Watts per unit volume or unit weight, which will be at -a minimum when their magnetization is oriented in this preferential direction.

This heterogeneity in the magnetic characteristics of the sheet complicates, meanwhile, the problem of the assembling of magnetic cores of the type considered in the corner zones where the winding legs are joined to the yoke; where it is a matter of obtaining, with the least possible disturbance or increase of electrical losses, a change in the direction of the flux lines which is generally equal to 90. There have already appeared, to this end, numerous and diverse shapes and methods of assembling sheets in successive layers to form ra magnetic circuit.

In one type of core which is now usedthe adjacent edges of the layers of the winding legs and the yokes are cut out and joined along an oblique line which makes an angle of around 45 with the optimum direction of the magnetic field in the respective sheets, and the oblique joints thus formed are placed at a different location in each successive layer in such a way as to produce an overlapping.

According to other techniques, which are still older,

an embodiment was provided in which elements in the form of an L were assembled by joining a winding leg layer and a yoke layer by welding along a joint having an oblique direction with respect to the optimum flux direction of each layer, the joint being occasionally formed by having the abutting edges of the two pieces in the form of a sawtooth in order to improve the strength of the weld. The magnetic circuit is produced, in this case, by the simple joining of two stacks of such L-shaped elements. e According to another, more recent suggestion, it has been attempted to improve the flow of magnetic iiux by adopting two different forms for the outlines of the joints or connecting borders between the two abutting sheets and by causing these two outlines to alternate from one layer to the next at each corner of the magnetic circuit. Among the several outline shapes contemplated Ifor certain of the abutting joints there is found in particular the sawtooth shape already mentioned above in the case of layers which Were assembled by welding.

These various prior solutions still present serious inconveniences: on the one hand they lead to serious prob- H table in all of the joints lems of fabrication concerning the work and tooling necessary for the cutting of the sheets as well as the assembling of the magentic circuit; on the other hand, despite these complications, these solutions do not permit the suppression to the greatest desirable degree of the additional losses which are attributable to the disturbances of the magnetic flux lines at the corners of the magnetic circuit and at the abutting joints between the sheets forming the successive layer-s thereof; experience shows that, in effect, even under the best operating conditions, the actual results remain extremely disappointing, revealing increases of losses of 25 to 50% compared with the values which are known to exist in the absence of joints.

The present invention is aimed at avoiding these inconveniences by offering the advantage of causing the cutting and assembling ofthe sheets to be simpler and more economical, and especially by presenting the possibility of rendering almost negligible the undesirable effects of the disturbances in the corners of the magnetic circuits.

A laminated magnetic circuit according to this invention is essentially characterized by the fact that in each of its corner zones, corresponding to the meeting of any pair of its branches, the abutting joint of each and every component sheet follows a staircase pattern composed of steps having sides which are oriented to follow substantially the longitudinal directions of the pair of branches under consideration.

Experience shows that such a systematic construction of joints in the form of steps of a staircase is capable of 'eading to a completely unexpected improvement in the performance of the magnetic circuit; it permits, in particular, reducing to a practically negligible amount the additional losses which had proved to be hitherto inevipreviously constructed.

The characteristics and advantages of this invention will be made clear, moreover, from the following description taken together with reference to the attached drawings in which FIGURE 1 is a vertical cross-sectional vview of the magnetic circuit of a single phase transformer;

FIGURE 2 is a detail view to a larger scale of one corner region of the unit of FIGURE 1;

FIGURE 3 is a view, similar to that of FIGURE l, showing a variation of the basic unit;

FIGURE 4 shows a three phase magnetic circuit;

FIGURE 5 shows an example of a magnetic circuit having widened yokes;

FIGURE 6 is a detail view case joint;

FIGURE 7 is a partially cross-sectional view of one example of an experimental embodiment of the magnetic circuit of a single phase transformer;

FIGURE 8 is a cross-sectional view taken along the plane VIII-VIII of FIGURE 7; and

FIGURE 9 is a graph showing the relative losses in a transformer whose core is constructed according to FIGURES 7 and 8.

Following the selected embodiment shown in FIGURE 1, the concept of the present invention is applied to the construction of the magnetic circuit of a single phase transformer of a generally rectangular shape having two cores, or winding legs, 11 and 12, adapted to receive several windings (not shown), and two yokes, 13 and 14; each of the four branches, 11-14, is constructed from a stack of sheets cut in bands from a sheet of grain oriented material so that there is thus presented a preferential direction of the flux lines which is indicated by the arrows P.

If one, considers, for example, the yoke 13, one sees that it iscomposed of sheets, such as ABCD, of a genof a variation of the stairerally trapezoidal form, with a large base AD along the exterior side, a small base BC along the inner side, and two latenal sides AB and CD, the latter being cut in a staircase pattern with the treads and the risers being of practically equal length parallel to and perpendicular to the preferential direction P. To each sheet of the yoke thus constructed there is attached a winding leg sheet 12 which is cut out along A1-B1-C1-D1 and a winding leg sheet 11 which is cut out along A3-B3-C3-D3, while another yoke sheet 14 is inserted at A2-B2-C2-D2. There are thus constructed four staircase joints su-ch as A-D3- -B-C3; Al-D- B1-C; etc., each of these joints being entirely disposed to one side of the diagonal of the corner Zone deined as the zone of overlap which would be produced by extension of the longitudinal borders of the adjacent branches. For example, every point of the staircase joint A-D3- -B-C3 is found to be above the diagonal A-C3, while every point of the joint A1-D -Bl-C is found to be below the diagonal Al-C, and so forth.

According to one embodiment each of the legs, or branches, of the magnetic circuit consists of a simple stacking of similar sheets according to FIGURE l; the different branches thus formed are then fitted together, the joints of each of the layers being in alignment with the corresponding joints -of all of the other layers of the circuit. This form of construction obviously :constitutes a considerable simplification in the construction and, should the need arise, in the repair or modiication of the device, especially with regard to adding or replacing the windings. In this case the overlapping of joints is entirely done away with.

The staircase shape of the joints leads to a surprising reduction in losses, as will appear from the performances of certain experimental embodiments, the results of which will be set forth further along in the specification. One can attempt to explain this remarkable phenomenon 'by supposing, particularly, that the length of the iiux lines which are perpendicular to the preferential direction in the vicinity of the corners (thus perpendicular to the direction of small losses and high permeability) tinds itself in some manner divided by the number of tiers of the staircase. By referring to FIGURE 2, where there has been drawn, to one side of the diagonal A-C3, a line M-M which is parallel to the diagonal and whi-ch divides the staircase joint into two equal parts, one can consider that the portions where large losses occur will be found to be reduced to the shaded areas which extend between the line M-M and the steps of the staircase joint.

One will thus seek, in general, to increase the number of steps to the limit permitted by the manufacturing equipment, the more so as the circuit becomes larger.

One can even envisage, according to a variation of this invention, to construct a magnetic circuit by the assemblage of elemental strips having a width equal to one step of the joint, as is suggested in FIGURE l by the thin lines t1, t2, t3, and t4. In this case, each leg of the circuit will be constructed by placing side by side a certain number of prismatic blocks of various lengths for example parallelepipeds, with their long dimensions arranged in echelons, or steps, in order of increasing length; each of these blocks itself being formed by the stacking of a desired number of rectangular strips.

When it is desired to construct with overlapped joints, it will be preferred to utilise, according to this invention, layers which alternate between the arrangement shown in FIGURE 1, land that shown in FIGURE 3, the latter arrangement being obtainable either by a turning over or by a simple translation in a lengthwise direction of all of the sheets in one or several layers of the structure of FIGURE l. As one can see from FIGURE 3, where the joints of the layers constructed according to FIGURE 1 are shown in dotted lines at each corner, the entire staircase joint of each layer will appear on one side or the other of its diagonal, with the side on which it appears alternating from layer'to layer or from group of layers to the next group.

FIGURE 4 shows one modification of this invention which can be used to construct the magnetic circuit of a three phase transformer. The exterior winding legs 21 and 22 of this circuit meet the yokes 23 and Z4 along joints which are similar to those which have already been described in connection with FIGURES 1 and 2, the nature of any eventual overlapping being indicated by dotted lines. The central winding leg 25 is composed of layers, cut in the form indicated, which are fit into corresponding layers of the yokes to form the staircase joints, these joints being formed alternately in each successive layer, on alternating sides of the diagonal-s EF, GF, H] and KJ of corner zones like E-El-F-Fl, F-Gl-G-Fl, etc. Here again, one can adopt either a construction without overlapping joints similar to that shown in FIGURE l, or a construction with overlapping joints; in the latter case the sheets of successive layers, or successive groups of layers, will alternatively take the positions represented by the solid staircase lines and those represented by the dotted lines. One will observe that the positions described by this second group of lines are derived from the positions shown by the solid lines simply by a translation of each of the legs 21 to 24 and a rotation of the leg 25 about an axis through the points F and J, or more simply by a rotation of one layer, or a group of layers, about said axis through F and J.

FIGURE 5 shows a modiication of the single-phase core having two cores, or winding legs 31 and 32 and two yokes 33 and 34, which differs from those shown in FIGURES l and 2 in that lthe width of the yoke layers exceeds that of the winding leg sheets by a given amount L. In this case the joints are laid out to one side of 45 diagonals, such as QP1 extending from the inside corners of the circuit, of the square zones such as Q-P1-P-Q1 which squares are derived by ignoring the added width L Iof the yokes. In case overlapping is employed, it can be seen that the second orientation of elements (indicated in dotted l-ines) is obtainable lby a lengthwise shifting of the Winding leg sheets and a rotation of of the yoke sheets about an axis which is parallel to the length of the winding legs and which lies lin the plane of the ligure.

In all of the embodiments described albove the staircase joints followed diagonals of corner regions which were, in fact, square; these diagonals-which could also be referred to as base lineswere thus the bisectors of the longitudinal axes of the two adjacent sheets and made an angle of 45 with them; in addition, each of the steps of each staircase joint had two equ-al edges. This arrangement seems, in fact, to be preferable and is well adapted to simplify the fabrication of the circuit. Nevertheless, this invention is not limited to such a form, but encompasses in particular the possibility of establishing, on one side or the other of base lines, such as the diagonal P-QZ of FIGURES 5 and 6, staircase joints, each edge of which has a length proportional to the cosine of the angle which it forms with its respective diagonal or base line (cf. FIGURE 6). Some modifications could also be envisaged in the profile the steps wherein their tops (corners) are slightly rounded or bevelled.

In the ygeneral case illustrated in FIGURES 5 and 6 one will be able to use sheets having higher losses for the yokes because the iiux density will be reduced there in proportion to the amount by which that branch is widened. yIt can therefore be concluded that the usef-ul embodiments of this invention are not limited to those forms using grain oriented sheets for all of the branches.

As an illustrati-on of the quality of perfonmance obtainable by virtue of the present invention, the results obtained with an experimental core will be described in connection with FIGURES 7 to 9.

FIGURES 7 and 8 show in a detailed manner, and with the dimensions shown in millimeters, the precise form of the magnetic circuit for a single phase transformer which was constructed from sheets of ARMCO grainoriented steel having a thickness of 0.35 mm. (0.014 inch) with ends which have been cut according to a staircase pattern, each edge of which has a length of 10 mm. (0.4 inch). 'Ihe circuit was square in shape, with each exterior edge having a length of 465 mm. (18.3 inches).

Three circuits of similar dimensions were constructed for purposes of comparison, each being constructed in a different manner:

(I) One construction was made for the purpose of providing reference, or control data as to the efficiency of prior art circuits. This circuit was made with overlapping rectangular sheets forming the well-known rightangle joints. The rectangular sheets were produced by extending the strips shown in FIG. 7 to the outer borders of the circuit, as is suggested by the broken-line extensions P1 and P2 of that figure.

(II) A second construction was made using staircase joints, without any overlapping, according to t-he teachings associated with FIGURE 1 above.

(III) The third circuit was made with voverlapped staircase joints yfollowing the teachings associated with FIGURE 3, above.

In FIGURE 9, the curves represent:

T: the curve of the inherent losses in a solid untreated sheet of the material used in the manufacture of these circuits, as indicated by the manufacturer of the sheets, expressed in watts/kg. vs. fiux density (B) in gauss;

I, II, III: the experimental lcurves, in the same units, the respective simil-arly numbered circuits described above, as measured in the laboratory.

'Ihese curves were derived from data obtained with a windin-g of 21 turns on one winding leg of the magnetic circuit and a winding of turns on the other Winding leg thereof.

The graph shows that, 15000 gauss for example, the increased losses due to the presence of joints equals 1.80 w./kg. for the reference construction, decreases to 1.45 w./kg. for the device made with staircase joints without overlapping, as in construction II, and diminishes still further to 1.19 W./kg. for construction III, the model utilising the staircase j-oints and overlapping suggested by FIGURE III, while the minimum possible losses for this material have been determined by the manufacturer to be equal to 1.13 at this fiux density. In other words, the joints of a typical prior art construction caused the magnetic circuit losses to increase by more than 59% while the joints of the present invention caused losses to increase by only 28% in the simpler embodiment of FIGURE 1 and by only 5% for the embodiment of FIGURE 3. Even without the use of overlapping joints, the simpler embodiments of the present invention compare favorably with the best of the prior magnetic circuits, while the modification employing the technique of overlapping joints permits the losses in the resultant circuit to approach the theoretical minimum. A surprising improvement is thus realized over the results obtainable by devices Constructed according to the prior art techniques. It is quite remarkable to note that .for constructions II and III the deviation from the minimum possible losses T tends to diminish more as the values of ux density increase, becoming almost imperceptible, in the case of construction III, at around 18,000 gauss. It is even more remarkable to note, for another thing, that these results were obtained with unannealed sheets, in other words, the sheet-s had not yet undergone the usual treatment employed to compensate for the hardening which results from the manipulation and the cutting, and which is the cause of additional losses.

The invention described herein is not intended to be limited by the specific embodiments shown. Many modifications are possible without departing from the spirit thereof. For example, the form of the staircase joint could be slightly modified so as to be irregular in shape at one or all of the corners. Various other modifications will occur to those skilled in the art. Therefore the embodiments shown herein should be considered as exemplary, and not limitive of the present invention.

What is claimed is:

1. A laminated magnetic circuit for electrical devices, such as transformers, comprising at least one polygonal frame member having a plurality of branches each defining one side of said member, each of said branches being composed of a plurality of stacked sheets, each having a short inner longitudinal edge, a long outer longitudinal edge, and two lateral edges, with each said sheet in each said branch being coplanar with a corresponding sheet in every other one of said branches, and with each lateral edge of each said sheet abutting against the adjacent lateral edge of the corresponding sheet in a respective adjacent one of said branches to form a joint, each said lateral edge defining said joint having a staircase configuration defined by a plurality of successive straight edge sections, with every other one of said sections extending parallel to the longitudinal dimension of one of the sheets whose lateral edge defines said joint and the remaining ones of said sections extending parallel to the longitudinal dimension of the other one of said sheets Whose lateral edge defines said joint.

2. An arrangement as defined in claim 1 wherein, at each corner of said frame member, each of said joints is disposed along, and to one side of a diagonal of the rectangular region enclosing said joint and defined by the outer longitudinal edges and the extensions of the inner longitudinal edges of said sheets forming said joint.

3. An arrangement as defined in claim 2, wherein, at each corner of said frame, all of said joints are disposed in alignment with one another and on the same side of said diagonal.

4. A magnetic circuit as recited in claim 2 wherein each of said rectangular regions are square in shape, so that said diagonal forms a 45 angle wit-h the longitudinal direction of each of the adjacent branches.

5. A magnetic circuit as recited in claim 1, wherein all of said sections of each said lateral edge are equal in length.

6. A magnetic circuit as recited in claim 2 wherein the staircase joints in all but two adjacent corners of said frame member are disposed alternately, from one layer of sheets to the next on opposite sides of their diagonal in such a way that the joints in one layer of sheets are displaced with respect to, and overlap, those of the adjacent layers.

7. A laminated magnetic circuit comprising a series of rectangular layers, each comprising four branches of generally trapezoidal configuration, the boundaries of each said branch being constituted by a long base, a short base, and a pair of oblique ends, each of said ends being cut in the form of a staircase comprising a series of steps the component edges of which are alternately perpendicular to and parallel to the bases of said branches, with all of said parallel edges being of equal length and all of said perpendicular edges being of equal length, eac-h of said branches being joined at its ends to corresponding ends of its adjacent branches by the imbricating of the steps of each pair of abutting ends to form a staircase joint at ea-ch corner of each of said rectangular layers.

8. A magnetic circuit as recited in claim 7 wherein, at least at bot-h ends of one of said branches, all of the steps of each staircase joint lie entirely to one side of a base line extending diagonally from the junction point of the short bases to the junction point of the long bases of the ltwo branches forming said joint.

9. A magnetic circuit as recited in claim 7 wherein all of the steps of each staircase joint lie entirely to one side of a base line passing through the junction point of the short bases of the two adjacent branches and extending at an angle of 45 to each of said short bases.

10. A magnetic circuit as recited in 'claim 8y wherein, at each corner of said circuit, the staircase joints of successive layers lie on alternate sides of said base line.

11. A magnetic circuit as recited in claim 9 wherein, at each corner of said circuit, the staircase joints of successive layers lie on alternate sides of said base line.

12. A laminated magnetic circuit comprising two yoke branches, two external leg branches and at least one intermediate leg branch parallel to said external leg branches, each of said branches being made-up by the stacking of a succession of layer-forming sheets; said yoke and external leg branches being assembled at four corner zones into an outer closed frame of generally rectangular shape, this assembling being made along corner base lines extending from each corner point of the inner contour of said frame to the outer contour, whereas said intermediate leg extends at each end within the adjacent yoke branch along two intermediate base lines dening an `isosceles triangle with that portion of the inner side of said adjacent yoke branch which is intercepted by the two longitudinal sides of said intermediate leg; each butt joint between any two adjacent sheets of any given layer being in the shape of a staircase pattern built upon and to one side of a respective one of said base lines; wherein, an observer following a closed path along the four sides of said outer frame will meet each joint in succession with each joint being disposed on a same side relatively to its respective base line.

13. A laminated magnetic circuit as recited in claim 12, wherein, for all but the joints associated with one of said yoke branches, each said staircase joint associated with a given base line is disposed on alternate sides thereof in successive layers of said circuit, all of said staircase joints associated with each base line of said one yoke branch being disposed to the same side of their associated base line.

References Cited by the Examiner UNITED STATES PATENTS 2,393,038 1/1946 Forbes 336-217 2,407,626 9/1946 Welch 336-217 X FOREIGN PATENTS 735,228 8/ 1955 Great Britain.

337,271 5/ 1959 Switzerland.

LARAMIE E. ASKIN, Primary Examiner. ROBERT K. SCHAEFER, Examiner.

T. J. KOZMA, Assistant Examiner. 

1. A LAMINATED MAGNETIC CIRCUIT FOR ELECTRICAL DEVICES, SUCH AS TRANSFORMERS, COMPRISING AT LEAST ONE POLYGONAL FRAME MEMBER HAVING A PLURALITY OF BRANCHES EACH DEFINING ONE SIDE OF SAID MEMBER, EACH OF SAID BRANCHES BEING COMPOSED OF A PLURALITY OF STACKED SHEETS, EACH HAVING A SHORT INNER LONGITUDINAL EDGE, A LONG OUTER LONGITUDINAL EDGE, AND TWO LATERAL EDGES, WITH EACH SAID SHEET IN EACH SAID BRANCH BEING COPLANAR WITH A CORRESPONDING SHEET IN EVERY OTHER ONE OF SAID BRANCHES, AND WITH EACH LATERAL EDGE OF EACH SAID SHEET ABUTTING AGAINST THE ADJACENT LATERAL EDGE OF THE CORRESPONDING SHEET IN A RESPECTIVE ADJACENT ONE OF SAID BRANCHES TO FORM A JOINT, EACH SAID LATERAL EDGE DEFINING SAID JOINT HAVING A STAIRCASE CONFIGURATION DEFINED BY A PLURALITY OF SUCCESSIVE STRAIGHT EDGE SECTIONS, WITH EVERY OTHER ONE OF SAID SECTIONS EXTENDING PARALLEL TO THE LONGITUDINAL DIMENSION OF ONE OF THE SHEETS WHOSE LATERAL EDGE DEFINES SAID JOINT AND THE REMAINING ONES OF SAID SECTIONS EXTENDING PARALLEL TO THE LONGITUDINAL DIMENSION OF THE OTHER ONE OF SAID SHEETS WHOSE LATERAL EDGE DEFINES SAID JOINT. 